The invention relates to a process for assessing the purity of 5-ethylidene-2-norbornene, and correlating impurity levels to improved polymerization reactions, including improved catalyst efficiencies. The invention also relates to purification methods, and to compositions comprising 5-ethylidene-2-norbornene and low levels of each impurities. In addition, the invention relates to polymerization processes as described, and to polymers formed from such processes and compositions containing the same.
The diene, 5-ethylidene-2-norbornene (ENB), is a critical raw material for making ethylene-propylene-diene modified (EPDM) polymer in solution and gas phase polymerizations. In these polymerizations, ethylene, propylene and ENB are ter-polymerized to produce the EPDM. In a typical EPDM, the amount of ENB varies from about 0.1 weight percent to about 15 weight percent, depending upon the particular polymer being manufactured.
The ENB is typically manufactured in a two step process. In the first step, cyclopentadiene and butadiene undergo a Diehls-Alder reaction to yield vinyl norbornene. In the second step, the vinyl norbornene is isomerized to ENB with an active metal or a basic catalyst. A reaction schematic of the two-step process is shown below.

The quality of the ENB is critical for good catalyst efficiency in an EPDM polymerization. Thus, the ENB must be produced and purified, so that residual compounds (like cyclopentadiene), which can act as catalyst poisons, are present at very low levels. Additionally, the ENB must be protected from air, since it is highly reactive with oxygen, which leads to gum formation (polyENB) and oxygenated ENB derivatives. ENB is usually stored in an inert atmosphere, such as nitrogen, to maintain its oxidative stability. In addition, radical scavengers or inhibitors, such as 4-tert-butylcatecol (TBC) and/or 2,6-di-tert-butyl-4-methylphenol (BHT) may be added to the ENB to inhibit side reactions.
The quality of ENB is assessed by a variety of conventional analyses, such as Gas Chromatography (GC), colorimetric analysis and water analysis. The properties measured by these conventional ENB analyses are typically used to set the specification criteria for suitable lots of ENB. However, often lots of ENB that meet the criteria of all of the typically employed analyses, perform poorly in catalyzed polymerization reactions. The failure of conventional ENB analyses to discriminate between ENB that yields acceptable catalyst performance and ENB that does not, indicates that the sensitivities of these conventional analyses are not sufficient to detect inhibitory levels of impurities and/or that these conventional analyses are not measuring all of the impurities that inhibit catalyst efficiency.
Applied Analytics, Inc. advertised (Process Anaylzers Newsletter, February 2006) a rapid, on-line, detection method of impurities in 5-ethylene-2-norbornene by photodiode array spectroscopy. This method was disclosed as being capable of rapidly determining the presence of an impurity by monitoring the absorbance at 320 nm and an internal reference at 343 nm. However, no characterization of the 5-ethylene-2-norbornene, in reference to polymerizations or polymerization catalyst efficiencies was provided.
There is a need to develop more sensitive characterization methods to access the quality of ENB, typically used in lots for polymerization reactions. There is also a need to optimize such polymerization reactions. In addition, there is a further need to develop such methods to monitor ENB purification processes. Moreover, there is a need to examine and correlate the effect(s) of certain ENB impurities, which current analytical tools do not examine, on polymerization catalyst efficiencies. These issues and others are addressed by the following invention.